Nitrogen trifluoride thermal cleaning apparatus and process

Abstract: The present invention is a method and apparatus for the dynamic cleaning of semiconductor fabrication equipment and particularly quartzware with thermally activated nitrogen trifluoride wherein the cleaning effluent is safely removed and cleaning by-products isolated or diluted to provide for efficient cleaning and rapid restarts of fabrication equipment so cleaned.

Description: The invention relates to an apparatus for cleaning materials and/or equipment surfaces in semiconductor manufacturing using nitrogen trifluoride according to the opening clause of claim 1 and a corresponding cleaning process. Generally the present invention is directed to the field of thermal cleaning with nitrogen trifluoride etchant. More specifically, the present invention is directed to cleaning various silicon-containing semiconductor substances from wafers and chemical vapor deposition equipment including quartz vessels and hardware using a dynamic flow of nitrogen trifluoride at elevated temperatures with a unique vacuum and removal system and process. The semiconductor industry has experienced a long-felt need to solve the problem of cleaning chemical vapor deposition furnaces and quartz tubes in the furnaces as well as quartz hardware of various undesired substances such as silicon nitride, polycrystalline silicon, titanium silicide, tungsten silicide and various other silicides as well as silicon dioxide which are typically present as undesired films on furnaces and quartz hardware because of their deposition on silicon wafers and chips being processed as electronic materials and integrated circuits. The normal procedure for cleaning is to remove the parts, such as those made of quartz, metals or other materials from a furnace, such as quartz furnace tubes, and perform a wet chemical cleaning. O-ring seals would typically have to be replaced in such an operation, as well as cleaning of lines, doors and other vacuum components. Another alternative is to use another piece of equipment and perform a plasma cleaning. The wet chemical cleaning is very costly and time consuming. When the equipment is shut down to pull the quartz parts, it can require up to 18 hours of time. Also, the system necessitates reverification for its operating integrity before it can be used again. Direct cleaning application requires special chemicals, equipment and sinks to perform this cleaning. Another disadvantage is that the quartzware is attacked at accelerated rates which affects its reproducibility and reliability of operation. This is especially true when cleaning quartz racks or wafer holders. These components have special slots cut in the quarts to hold the parts being coated, and when the wet chemical clean attacks the quartz, it affects the dimensions of these slots. When the slots are affected, the parts being held are not coated uniformly, which requlres the quartz be replaced at accelerated scheduling. The plasma cleaning method requires the use of another piece of equipment especially designed to perform a cleaning of quartz tubes in place within the chemical vapor deposition furnace equipment. First, the plasma cleaning method does not clean the other quartz parts which are used in the chemical vapor deposition furnace system. This means these parts will need to be chemically wet cleaned, separate and apart from plasma cleaning methods. Also, the plasma cleaning equipment takes up space in the manufacturing area, and may prevent other tubes from being used in the system while it is being utilized. If the quartz parts are replaced with another material like silicon carbide, it will make the plasma system application unreliable. Methods of using nitrogen trifluoride have been attempted but never have been brought to the marketplace. One such method was performed in a static mode that allowed by-products to condense on the cooler walls of the system. This caused the dangerous condition when these by-products were not evacuated before returning the system to the atmosphere. This called for extended purging times and reduced the benefits of this method. It also allowed for possible dangerous gas mixtures to develop in the system's vacuum components and may mix with gases which are normally utilized to deposit films on the wafers. One nitrogen trifluoride cleaning method is discussed in UK Patent Appln. GB2183204 where nitrogen trifluoride is used in a static mode and suggestion for use in a continuous flowing mode is also set forth. This patent application does not address the means or methods for removing cleaning by-products or the treatment of by-products once removed. An apparatus for cleaning material and/or equipment surfaces in semiconductor manufacturing as acknowledged in the opening clause of claim 1 is known from Patent Abstracts of Japan, JP-A-1-306580 (Derwent Patent Abstracts), No. 90-027429). Furthermore it is known from the Journal of Vacuum Sciency and Technology, (A10, 1992, pages 3376-7) to use a vacuum venturi to evacuate and cycle purge corrosive, toxic, and flammable gases. The prior art has failed to address a commercially successful process or apparatus for cleaning semiconductor materials or equipment using a gaseous source to produce volatile cleaning by-products which are readily removed from the materials or equipment after cleaning is accomplished. In addition, the prior art has not addressed a viable method or apparatus for removal of cleaning by-products and collection of such by-products (which typically may be reactive and toxic) for safe, easy disposal when servicing chemical vapor deposition equipment and materials treated in such equipment. The apparatus as defined by claim 1 and the process as defined by claim 14 overcome these drawbacks of the prior art. Suitable embodiments of said apparatus are defined by the features of subclaims 2 to 13 and suitable embodiments of said process are defined by the features of subclaims 15 to 23. The invention will be described referring to the enclosed schematic drawings in which FIG 1 is a schematic illustration of an embodiment of the cleaning apparatus of the present invention using a cold trap and a vacuum venturi. FIG 2 is a partial schematic illustration of an alternative means for carrying out the claimed process to the FIG 1 embodiment of the cleaning apparatus of the present invention shown in FIG 1 wherein vacuum is provided by a mechanical vacuum pump. FIG 3 is a partial schematic illustration of the cleaning apparatus of the present invention shown in FIG 1 wherein no cold trap is utilized and a heated gas is used in the vacuum venturi. FIG 4 is a partial schematic illustration of an alternative means for carrying out the claimed process to the FIG 1 embodiment of the cleaning apparatus of the present invention shown in FIG 1 wherein no cold trap is utilized and a heated mechanical vacuum pump and disposal lines are used. An apparatus and process have been developed for in-situ cleaning of process chambers, boats and/or puzzle pieces in a semiconductor electronic fabrication facility. The present invention uses, preferably, a vacuum venturi with heated process lines and means to heat and temperature control a pressurized gas as a motive fluid for the venturi to remove the waste products of the cleaning from a process chamber, or alternatively, a vacuum venturi pump and a cold trap apparatus with heated process lines connecting the cold trap to the process chambers, etc. for remote pumping and simultaneous exhaust dilution of waste products of cleaning. A mechanical rotary or reciprocating vacuum pump can also be used as the vacuum means, with heated process lines. Cleaning is performed with thermal energy to decompose nitrogen trifluoride gas for generation of fluorine cleaning reagent. The present invention uses a dynamic pressure control to clean the deposition materials from the previously coated material or equipment surfaces, such as quartz hardware. The present invention is also capable of cleaning components downstream of a process chamber outside an elevated temperature or thermal zone. The present invention can be retrofitted to existing semiconductor process deposition equipment, integrated into new equipment, or can be built as a stand-alone process tool for cleaning of parts. The present invention reduces the cost to clean commonly used quartzware parts and metal roughing lines used in semiconductor and electronic manufacturing equipment by allowing their surfaces to be cleaned in-situ without removal of surfaces from the process system. The present invention does not require a retrofit that utilizes a radio frequency power supply and means of applying radio frequency to surfaces for activation energy to decompose nitrogen trifluoride to produce cleaning reagent. The present invention also does not require the existing system pumping apparatus to be used to remove cleaning effluent. The present invention also eliminates the use of other equipment used for current methods of cleaning such as to remove quartzware or roughing lines for cleaning in aqueous acids and deionized water in large, semi-automated ventilated tanks. The present invention eliminates what chemical wastes and possible operator exposure to hazardous acids and solvents used in current cleaning systems. The present invention involves cleaning a typical process chamber including the parts arrayed within a chamber of a semiconductor or electronic fabrication facility by evacuating the chamber using a pressurized gas vacuum venturi, preferably supplied with heated and temperature controlled gas to provide a vacuum pressure of about 13330 Par (100 torr). Nitrogen trifluoride is then introduced via a gas supply means, such as a gas control manifold, into the process chamber and associated roughing manifold and the cleaning process is conducted at a pressure of about 79980 par (600 torr) using the thermal energy of approximately 100° to 650°C, preferably 400° to 475°C, more preferably 425°C available from the existing equipment heating system to decompose or disassociate the nitrogen trifluoride and produce a fluorine cleaning reagent, such as ionic or free fluorine. The fluorine cleaning reagent produced from the decomposition or disassociation of nitrogen trifluoride under thermal degradation are effective against deposits of silicon nitride, polycrystalline silicon, titanium silicide, tungsten silicide, refractory metals and their various silicides. The fluorine cleaning reagent produced from the decomposition or disassociation of nitrogen trifluoride has minimal effect on quartz tube furnaces or quartzware used within such furnaces. Upon completion of the cleaning process, the nitrogen trifluoride source is turned off and the system pumped via the pressurized gas vacuum venturi, preferably with heated and temperature controlled pressurized gas, for 15 minutes followed by a purge with nitrogen for at least one-half hour while under vacuum. The cleaned process chamber is then isolated from the cleaning apparatus comprising a nitrogen trifluoride source and pressurized gas in vacuum venturi evacuation system and is evacuated and cycle purged using nitrogen while using the process chamber's own pumping system for approximately one-half hour prior to the return of service in the semiconductor or electronic fabrication procedure. The most significant feature of the present invention is that the process is executed in a dynamic flow mode using a nitrogen or other pressurized inert gas driven vacuum venturi pump. Preferably, the pressurized inert gas is heated and temperature controlled to be above the condensation temperature of the waste products, such as 100°C. The advantage of this type of a pump ensures that minimal cleaning gas effluent, nitrogen trifluoride and its degradation products, may come into contact with the process equipment system pumping stack. This provides a safe, efficient and effective process and apparatus for the cleaning of process chambers or zones and supporting fixtures and appliances included in such chambers and zones as well as materials such as wafers. Typically the nitrogen trifluoride can be thermally activated to degrade and produce the fluorine cleaning reagent at elevated temperatures between 100 and 650°C, preferably 400° to 475°C, more preferably 425°C. In addition, the use of the pressurized gas vacuum venturi, preferably with heated and temperature controlled pressurized gas, to induce vacuum during the cleaning procedure prevents possible dangerous gas mixtures, such as silicon hydride, oxygen and hydrogen from developing due to residual gases left in the process chamber's vacuum pumps. The use of heated evacuation lines, such as by heating tape, along with the dynamic method of flowing nitrogen trifluoride during the cleaning process, allows by-products from the cleaning cycle to be evacuated from the process chamber and not condense on cooler surfaces of the main vacuum system of a process chamber, thus preventing past problems and safety concerns associated with the use of nitrogen trifluoride as a cleaning gas. The pressurized gas vacuum venturi may work off a high pressure gas, such as nitrogen or argon, or any high pressure gas compatible with the system materials. The vacuum venturi may itself be heated or the gas used to create the vacuum may be heated, such as by heat tape on the conduits leading the gas into the venturi. In addition, by using the vacuum venturi operated by the pressurized gas, such as an inert gas, the process and apparatus of the present invention provides a natural dilution for the exhaust gases emanating from the cleaning of a process chamber with nitrogen trifluoride. This provides a safer exhaust method than past methods have utilized, by using an independent vacuum exhaust system from the vacuum system typically provided for a process chamber of a semiconductor manufacturing facility. In an alternative embodiment, the present invention also can use a cold trap, typically operated with cooling water, to condense volatiles removed by the cleaning operating using nitrogen trifluoride. Mechanical refrigeration can also be used to operate the cold trap, or alternatively cryogenic fluids can be used. By passage of such cleaning exhaust through heated vacuum lines to a cold trap, it is possible to isolate these toxic or reactive volatiles of the cleaning process in a centralized location for appropriate treatment and disposal. Any volatiles which do not condense in the cold trap are highly diluted by the pressurized gas in a vacuum venturi and can be subjected to further scrubbing in appropriate stack apparatus as is traditional in the industry. When a cold trap is used prior to a vacuum venturi or mechanical vacuum pump, it is not necessary to heat the vacuum venturi or its motive gas or the mechanical vacuum pump because the bulk of the condensable waste products are removed in the cold trap. With reference to the drawing in FIG 1, an embodiment of the present invention will now be set forth. A semiconductor manufacturing furnace 10 is illustrated containing, for example, 3 parallel quartz furnace tubes 12, 14 and 16 where various chemical vapor deposition processes are conducted on materials placed within the quartz tubes typically in various quartzware appliances or wafer carriers. Process gas is introduced from source 18 through manifold 20 and by various valves not illustrated through lines 22, 24 and 26 to the respective quartz tubes. Exhaust gases are collected in lines 28, 30 and 32, again appropriately valved but not illustrated, and centrally removed in manifold 34 to appropriate evacuation, scrubbing and downstream processing 36 of a typical semiconductor manufacturing facility. During the course of chemical vapor deposition of materials in the quartz tubes, deposition occurs on various appliances and carriers within the quartz tubes, as well as on the quartz tube surfaces themselves. At some point in time one or more of the appliances and/or tubes must be taken out of service for cleaning. Although in the present illustration the cleaning process will be exemplified by all of the quartz tubes being cleaned simultaneously, it is understood by appropriate manifolding, a quartz tube or appliances may be independently or separately cleaned while other tubes remain in service. After the furnace 10 is removed from manufacturing service for cleaning, pressurized nitrogen gas from source 52 is introduced by an appropriate valved conduit into a vacuum venturi 54 and exhausted through downstream scrubbing and vent system 56. This induces a vacuum in line 50 and the illustrated upstream equipment to produce a vacuum in the quartz tubes 12, 14 and 16. The tubes are maintained at an elevated temperature of approximately 425°C by the traditional heating system of furnace 10 used during normal manufacturing processes. Nitrogen trifluoride from a source 58 is introduced through open valve 60, line 62 and open valve 64 through manifold 20 and one or all of the connecting lines 22, 24 and 26 of the quartz tubes. During this time by appropriate valving not illustrated, process gas from source 18 is turned off. The nitrogen trifluoride in the dynamic flowing mode at elevated temperature sufficient for thermal degradation of the nitrogen trifluoride to appropriate species of fluorine cleaning reagents attacks the previously deposited substances from the chemical vapor deposition of the processing manufacturing cycle to remove those substances as volatile by-products. The fluorine cleaning reagent produced by thermal degradation of nitrogen trifluoride has high reactive activity with silicon nitride chemical vapor deposition layers and polysilicon chemical vapor deposition layers, but has minimal reactivity with the quartz tubes or quartzware used as appliances and racks in the tubes. The reaction by-products from cleaning, as well as any undisassociated nitrogen trifluoride is removed in lines 28, 30 and 32 by the action of the vacuum venturi and collected in manifold 34. However, rather than being removed through the traditional downstream processing system 36, that system is isolated by appropriate valving not illustrated and the cleaning effluent gases or waste products are removed through heated (heat traced or heat taped 70) exhaust conduit 40, by open valve 38, wherein pressure is monitored by pressure gauge 42. The heat tracing 70 provides a heated line outside the elevated temperature furnace 10 so that volatiles in the cleaning effluent or waste products do not condense, but are removed to a cold trap 48 operated by cooling water or appropriate refrigeration means. The heat tracing is powered by appropriate electrical elements or resistance wires. The cold trap condenses most cleaning exhaust volatiles before removal by various collection means, filtration or change out of appropriate getters or adsorbents. The uncondensed components of the cleaning effluent or waste products are removed in line 50 to the vacuum venturi 54 where the remaining cleaning exhaust or waste products are highly diluted with 60 to 100 liters of pressurized nitrogen gas and removed by a downstream scrubbing and vent system 56 of traditional arrangement. After appropriate cleaning time is provided, valve 60 is closed and valve 68 is opened to provide a purge with an appropriate gas, such as inert nitrogen, from source 66 to flow through the piping system and the quartz tubes and again removed through the conduit 40, cold trap 48 and vacuum 54 for disposal in an appropriate scrubber and vent system 56. Similar purge gas can be provided through valve 44 and source 46 to clean the cold trap and vacuum venturi when they are isolated by valve 38 being closed. At the end of the purge, valve 68 is closed as well as valve 64 and the system can be further evacuated using the vacuum venturi 54. An alternative apparatus for carrying out the claimed process is illustrated partially with reference to FIG 2. In FIG 2, the portion of the downstream system from line 34 of FIG 1 is shown with corresponding part numbers in the 200 series. Waste products comprising reaction by-products and any undisassociated nitrogen trifluoride is removed in manifold 234 and bypasses the traditional system vacuum pump or downstream venting 236. Valve 238 is opened in heat traced 270 line 240 to remove the waste products to cold trap 248 which is supplied with vacuum from a traditional mechanical vacuum pump 272 connected to the cold trap 248 through line 250. The evacuated gas is treated in a downstream vent or scrubbing system via line 274. Pressure is monitored through gauge 242 and purge gas from 246 can be provided when valve 238 is closed by opening valve 244. The apparatus of the present invention is set forth in FIG 3 which is a partially illustration of the downstream system of FIG 1. With reference to FIG 3, manifold 334 corresponds to manifold 34 of FIG 1 and the same upstream equipment is assumed to exist for the FIG 3 embodiment. From the traditional downstream processing equipment 336, a heat traced 370 line 340 is controlled through valve 338 to remove waste products of the cleaning process. Pressure can be sensed through gauge 342. The waste products in line 350 enter the vacuum venturi 354 by the suction induced by the motive pressurized gas (ie., nitrogen) from source 352, which is heated by heat tracing 358. Alternatively, the pressurized gas can be heated in some other manner before it enters the venturi or the venturi itself can be heated. The heating and temperature control is designed to avoid condensation of corrosive or clogging waste products on the equipment before entering a downstream vent or scrubbing system 356, such as a water scrubber. A further version of a downstream system used for carrying out the claimed process with the system shown in FIG 1 upstream of manifold 34 is shown in FIG 4 where manifold 434 corresponds to manifold 34 of FIG 1. The upstream equipment is the same as described for FIG 1 and only the downstream equipment is changed and will be described here. Waste products are removed from the furnace being cleaned in manifold 434 and rather than being removed in traditional downstream system 436, the waste products are removed in heat traced 470 line 440 by opening valve 438. Pressure is sensed in gauge 442. Vacuum is induced in a mechanical vacuum pump 472 which is kept above the condensation temperature of the waste products and the discharge of the pump 472 passes through a heat traced 476 line 474 to an appropriate vent or scrubber. Again, water scrubbing is probably appropriate for the anticipated waste products of this nitrogen trifluoride cleaning. Purging of the downstream equipment can be accomplished through valve 444 and purge gas source 446. Appropriate venting, gettering or scrubbing, such as water scrubbing, can be used as the disposal means to which the vacuum venturi or mechanical vacuum pump discharges the waste products of the cleaning operation. It is possible that a dedicated disposal device can be used or if appropriate the house disposal device of the facility where the invention is used can be used if it is appropriate to the type and amount of the waste products. Having described the present invention with regard to a preferred embodiment, it is apparent that the nitrogen trifluoride cleaning process and apparatus of the present invention provides a number of benefits over the prior art, including: the ability to clean system components in place; reduction in maintenance down time for cleaning; lower cost of cleaning and capital investment to effect appropriate cleaning procedures; the elimination of wet chemical cleaning materials and procedures; providing a cleaning method which does not require recallibration of the process chamber or furnace of the semiconductor fabrication facility prior to reinitiation of production runs; provision of a safe method for cleaning by using an isolated evacuation system from the manufacturing process apparatus vacuum system; providing a beneficial method of cleaning system quartzware and boats with minimal damage and handling; providing a method to insure fast by-product removal and economic cleaning process cycles, and providing a method which allows for automatic dilution of cleaning exhaust or effluent with an inert dilution gas, such as nitrogen, helium or argon, while providing for a source of vacuum. In addition, the cleaning method and apparatus of the present invention can be used to clean other types of process equipment, including stand alone cleaning equipment, stainless steel door flanges, vacuum conduits, exhaust piping, equipment of stainless steel, aluminum and ceramic, etc. The present invention has been described with reference to a preferred embodiment, however, it should be appreciated that the full scope of the present invention should be ascertained from the claims which follow.

Claims: An apparatus for cleaning materials and/or equipment surfaces in semiconductor manufacturing. using nitrogen trifluoride, comprising: a) a gas supply means (18, 20) connected to a chamber (10) and suitable for supplying nitrogen trifluoride to said chamber (10) for cleaning materials and/or equipment surfaces in said chamber (10); b) a heated exhaust conduit (340, 350) suitable for removing waste products of nitrogen trifluoride and volatile reaction products formed from the reaction of undesired substances on the materials and/or equipment surfaces and said nitrogen trifluoride and/or fluorine cleaning reagents disassociated from nitrogen trifluoride, said conduit (340, 350) being connected to said chamber (10); c) a vacuum means (352, 354, 356, 538) communicating with said heated exhaust conduit (340, 350) for evacuating said chamber (10) through said conduit (340, 350) wherein said vacuum means (352, 354, 356, 538) is connected to a disposal means (48) for said waste products, characterized in that d) said vacuum means (352, 354, 356, 838) is a pressurized gas vacuum venturi (354) having a source (352) of pressurized gas with a heater (538) for heating said pressurized gas to a temperature above the condensation temperature of said waste products. The apparatus of Claim 1 having a cold trap (48) connected to said conduit (340, 350) for capturing and condensing said waste products from said conduit. The apparatus of Claim 2 wherein said pressurized gas vacuum venturi (352, 354, 356, 538) is connected to said cold trap (48) for evacuating said chamber (10) through said conduit (340, 350) and said cold trap (48). The apparatus of Claim 3 wherein said cold trap (48) is connected to said conduit (340, 350) through a valve (338) which can isolate said cold trap (48) from said conduit (340, 350). The apparatus of Claims 1 to 4 wherein said apparatus includes a chamber (10) for containing said materials and/or equipment for cleaning. The apparatus of Claims 1 to 5 wherein said apparatus attaches to a chamber (10) containing said materials and/or equipment for cleaning. The apparatus of Claims 1 to 6 wherein said disposal means is a a scrubber means (356) for removing said waste products from said apparatus. The apparatus of Claim 2 including a valved conduit for controllably introducing a pressurized gas into said vacuum venturi (354) to induce a vacuum in said apparatus. The apparatus of Claims 2 to 8 wherein said cold trap (48) has means for introducing a cooling medium into and through said cold trap (48) to indirectly heat exchange with said waste products. The apparatus of Claims 1 to 9 wherein said chamber (10) is a chemical vapor deposition furnace. The apparatus of Claims 1 to 10 wherein said heated exhaust conduit (340) is heated by electrical elements (370). The apparatus of Claims 1 to 11 wherein a quartz carrier is situated in said chamber (10) for holding semiconductor wafers for cleaning. The apparatus of Claims 1 to 12 wherein said heated exhaust conduit comprises a plurality of parallel connected conduits connected to said vacuum means (352, 354, 356, 538). A process for cleaning materials and/or equipment surfaces using nitrogen trifluoride in semiconductor manufacturing equipment having evacuation and downstream processing means (36) for the exhaust gases comprising (a) initially evacuating - with said evacuation and downstream processing (36) isolated - a zone (10) contacting said materials and/or equipment surfaces; (b) heating said zone (10) to an elevated temperature sufficient to disassociate nitrogen trifluoride; (c) flowing nitrogen trifluoride through said zone (10); (d) cleaning undesired substances on said materials and/or equipment surfaces by chemical reaction of said nitrogen trifluoride and/or fluorine cleaning reagents disassocated from nitrogen trifluoride with said substances to form volatile reaction products, and; (e) removing said volatile reaction products and any remaining nitrogen trifluoride as waste products from said zone (10) by subsequent evacuation of the zone (10) wherein said waste products are evacuated through a heated exhaust conduit (340, 350), rather than through the evacuation and downstream processing means (36). The process of Claim 14 wherein said waste products are evacuated using a pressurized gas vacuum venturi (352, 354, 356, 538). The process of Claim 15 wherein said pressurized gas is heated prior to passing through said vacuum venturi (352, 354, 356, 538). The process of Claims 14 to 16 wherein said waste products are evacuated to a cold trap (48) wherein said waste products are captured in said cold trap (48). The process of Claim 17 wherein said cold trap (48) is subsequently isolated from said zone (10) and said cold trap (48) is further evacuated to remove said waste products from said cold trap (48) for disposal. The process of Claims 15 to 18 wherein said waste products are diluted with said pressurized gas. The process of Claims 14 to 19 wherein said waste products are scrubbed and vented. The process of Claims 15 to 20 wherein said pressurized gas is selected from the group consisting of nitrogen, argon, helium and mixtures thereof. The process of Claims 14 to 21 wherein said zone (10) is purged with an inert gas after said subsequent evacuation. The process of Claims 14 to 22 wherein said initial evacuation is at a pressure of no greater than 26660 Pa (200 torr), said flow of nitrogen trifluoride is at a pressure of no greater than 86645 Pa (650 torr) and said heating is at a temperature of no greater than 650° C.

Inventors: ENGLE GEORGE MARTIN, HULING BRUCE ALAN, SCHNEIDER CHARLES ANTHONY, ENGLE, GEORGE MARTIN, HULING, BRUCE ALAN, SCHNEIDER, CHARLES ANTHONY
Applicants: AIR PROD & CHEM, GEC INC, AIR PRODUCTS AND CHEMICALS, INC., GEC, INC.
Application year: 1994
Main classification: C23C16
IPC codes: B08B3, C23C16, H01L21, C11D7, B08B7